Abstract

We both theoretically and experimentally investigate the optimization of femtosecond Yb-doped fiber amplifiers (YDFAs) to achieve high-quality, high-power, compressed pulses. Ultrashort pulses amplified inside YDFAs are modeled by the generalized nonlinear Schrödinger equation coupled to the steady-state propagation-rate equations. We use this model to study the dependence of compressed-pulse quality on the YDFA parameters, such as the gain fiber’s doping concentration and length, and input pulse pre-chirp, duration, and power. The modeling results confirmed by experiments show that an optimum negative pre-chirp for the input pulse exists to achieve the best compression.

(a) Optimum RMS duration of the compressed-pulse and the corresponding transform-limited RMS duration as a function of pre-chirping GDD for the input pulse. Insets: compressed pulses and transform-limited pulses for three different pre-chirp. (b) bandwith evolution inside the Yb-fiber amplifier. (c) output sepctra for three different pre-chirp.

Calculated RMS duration of the optimum compressed pulse as a function of the FWHM pulse duration of the transform-limited Gaussian input pulse for three doping levels: blue-triangle curve for high doping at 1025/3 m−3; red-circle curve for medium doping at 1025 m−3; and black-square curve for low doping at 3 × 1025 m−3. The purple-diamond curve shows the compressed-pulse RMS duration obtained with a low-doping Yb-fiber amplifer seeded with transform-limited pulses.